U.S. patent number 3,817,226 [Application Number 05/284,547] was granted by the patent office on 1974-06-18 for fuel control system for internal combustion engines.
This patent grant is currently assigned to Nippondenso Co., Ltd.. Invention is credited to Kunio Endo, Hisato Wakamatsu.
United States Patent |
3,817,226 |
Wakamatsu , et al. |
* June 18, 1974 |
FUEL CONTROL SYSTEM FOR INTERNAL COMBUSTION ENGINES
Abstract
A fuel control system for internal combustion engines comprising
a first control signal generator to produce an output voltage
corresponding to an operating parameter of the engine, and a signal
processing circuit including a non-linear means for deriving from
the output voltage of the first control signal generator a
plurality of voltages having non-linear relation with the output
voltage of the first control signal generator, which are adjustable
to provide for a plurality of slopes corresponding to respective
subdivided portions of the fuel demand characteristic of the
engine, and an amplifier-adder to amplify and add together the
derived voltages so as to produce a total output voltage conforming
to the engine fuel demand characteristic over the entire range of
the engine-operating parameter. The pulse width of the pulse signal
to energize the fuel injection valves is varied in accordance with
the total output voltage from the signal processing circuit. Thus,
even if the fuel demand characteristic is non-linear, it may be
closely followed over the entire range of the involved
engine-operating parameter in controlling the amount of fuel
supplied to the engine.
Inventors: |
Wakamatsu; Hisato (Kariya,
JA), Endo; Kunio (Anjo, JA) |
Assignee: |
Nippondenso Co., Ltd.
(Kariya-shi, Aichi-ken, JA)
|
[*] Notice: |
The portion of the term of this patent
subsequent to September 19, 1989 has been disclaimed. |
Family
ID: |
26733350 |
Appl.
No.: |
05/284,547 |
Filed: |
August 29, 1972 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
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54681 |
Jul 14, 1970 |
3692003 |
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Current U.S.
Class: |
123/485; 123/492;
123/491 |
Current CPC
Class: |
F02D
41/10 (20130101) |
Current International
Class: |
F02D
41/10 (20060101); F02m 051/06 () |
Field of
Search: |
;123/32AE,32EA,139E,14MC,119R |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Goodridge; Laurence M.
Assistant Examiner: Flint; Cort
Attorney, Agent or Firm: Cushman, Darby & Cushman
Parent Case Text
CROSS-REFERENCES TO RELATED APPLICATIONS
This application is a continuation-in-part of application Ser. No.
54,681 filed on July 14, 1970 now U.S. Pat. No. 3,692,003.
Claims
We claim:
1. In combination with a fuel injection system for internal
combustion engines which is provided with one or more fuel
injection valves electromagnetically operated by a pulse signal
changed by an output voltage representing fuel demand of the
engine, produced based on at least one operating parameter of the
engine, a fuel control system comprising:
a control signal generator to produce an output voltage, the value
of said output voltage having a linear relationship with that of an
operating parameter of the engine,
a signal processing circuit, including non-linear means and linear
means, connected in circuit with said control signal generator,
said non-linear means producing at least one first voltage, the
value of which has a non-linear relationship with that of said
first output voltage, said linear means producing at least one
second voltage, the value of which has a linear relationship with
that of said output voltage, and
an amplifier-adder connected in circuit with said signal processing
circuit for amplifying and adding together said first voltage and
second voltage so as to produce the output voltage to meet the fuel
demand characteristics.
2. A fuel control system according to claim 1 further including
another control signal generator for producing an output voltage
when a value of another operating parameter of the engine satisfies
a predetermined value, the value of said output voltage being
constant, and said amplifier-adder being further connected in
circuit with said another control signal generator and amplifying
and adding together said first and second voltage and the output
voltage of said another control signal generator to meet the fuel
demand characteristics.
3. A fuel control system according to claim 1, wherein said
non-linear means comprise constant voltage diodes and
resistors.
4. A fuel injection control circuit for an internal combustion
engine having at least one electromagnetically operated fuel
injection valve which is held in an operative position by an
electrical pulse signal having a duration in time which is varied
as a function of the amplitude of a total output voltage, said
amplitude of said total output voltage varying in accordance with
fuel demand characteristics as a function of at least one operating
parameter of the engine, comprising:
a control signal generating means for producing an output voltage
which varies linearly with said at least one operating parameter of
said engine,
a signal processing circuit, including non-linear signal producing
means and linear signal producing means, connected to said first
control signal generator, said non-linear means receiving said
first output voltage and producing at least one first voltage which
varies non-linearly with said first output voltage, said linear
means producing at least one second voltage which varies linearly
with said second output voltage, and
adding and amplifying means connected to said signal processing
circuit for amplifying and adding together said first voltage and
second voltage so as to produce said total output voltage to meet
said fuel demand characteristics of said engine.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to fuel control systems for internal
combustion engines for controlling electromagnetically operated
fuel injection valves in accordance with operating parameters of
the engine.
2. Description of the Prior Art
The fuel control system of the type pertaining to the invention
usually uses an electromagnetic feedback type multi-vibrator
consisting of a pair of transistors and a feedback transformer to
provide for the feedback from the collector of one transistor to
the base of the other transistor of the multi-vibrator. The amount
of feedback, that is, the mutual inductance of the feedback
transformer is varied in accordance with the negative pressure in
the engine suction pipe, which is one of the engine operating
parameters, thereby varying the pulse width of the pulse output of
the multi-vibrator which faithfully follows the fuel demand
characteristic of the engine. The pulse output is impressed on the
fuel injection valve to drive it in such a manner that it is held
in the operative or open position for a period equal to the pulse
width, during which the fuel is injected either into the intake
manifold of the engine or directly into the cylinder.
As the means to vary the mutual inductance of the multi-vibrator in
accordance with the engine intake negative pressure is used a
movable iron core coupled to a diaphragm converting the change in
the intake negative pressure into a corresponding mechanical
displacement thereof, whereby the associated motion of the movable
iron core produces variation of the mutual inductance of the
multi-vibrator.
The fuel demand characteristic of the engine, however, is not
straightforward. By way of example, the relation between the engine
intake negative pressure and the amount of fuel to be supplied is
not linear but is represented by a particular curve. Therefore,
with the afore-mentioned conventional fuel control system the
movable iron core associated with the multi-vibrator should have an
extremely complicated configuration requiring very troublesome
manufacturing steps. Besides, such a movable iron core gives rise
to various problems in use such as mal-functioning due to external
vibrations to deviate from the proper fuel demand characteristic,
thus resulting in inferior reliability of the system.
Further, for engines having different fuel demand characteristics
the pitch of the windings of the feedback transformers, dimensions
of the diaphragm to convert engine intake negative pressure into
mechanical displacement and the configuration of the movable iron
core coupled to the diaphragm should be basically changed. In other
words, the above conventional system totally lacks in compatibility
with engines of different ratings.
An example of the conventional fuel control system in U.S. Pat. No.
3,005,447 granted to Gunther Baumann et al. on Oct. 24, 1961. This
patent comtemplates to obtain pulse signals each thereof having a
pulse width corresponding to a valve opening time which determines
the amount of fuel to be injected in the following way. In this
patent, the output pulse current from a pulse signal generating
circuit which is triggered by closing of a cam-driven contact is
made to flow through the primary winding of a transformer contained
in the circuit and the magnitude of a voltage induced in the
secondary winding of the transformer is changed according to a
variation in the mutual inductance caused by the displacement of a
movable iron core of the transformer driven by a pressure gauge
which is operated in response to intake manifold vacuum in an
engine. The secondary induced voltage is rectified and applied to
the base of a pre-stage transistor in the pulse signal generating
circuit in series with a DC bias voltage to control the
nonconductive period of the pre-stage transistor, which in turn
controls the duration of the output pulse current.
As seen from the above-described structure of the fuel control
system of the U.S. Pat. No. 3,005,447, it is clear that such a
system also contains all of the drawbacks of the conventional fuel
control system such as described above.
SUMMARY OF THE INVENTION
An object of the invention is to provide a fuel control system for
internal combustion engines comprising a first signal generator to
produce a voltage output corresponding to an operating parameter of
the engine, and a signal processing circuit to modify the output of
the first signal generator to introduce a non-linear character
approximating the fuel demand characteristic of the engine by
deriving from the output of the first signal generator a plurality
of modified output components through respective circuits each
providing an output pattern peculiar to a corresponding one of a
plurality of subdivided parts of the engine fuel demand
characteristic over the entire range of the involved
engine-operating parameter and amplifying and adding together the
respective derived voltage components through an amplifying means,
whereby the pulse width of the pulse signal impressed on the fuel
injection valve is varied in accordance with the voltage output of
the signal processing circuit to meet the entire engine fuel demand
characteristic.
According to the invention, an excellent advantage is featured in
that the pulse width of the pulse signal impressed on the fuel
injection valve can be continually and exactly varied in accordance
with a non-linear engine fuel demand characteristic over the entire
range of the engine-operating parameter, thus enabling exact
control over the amount of fuel supplied to the engine in
accordance with the fuel demand characteristic of the engine with
an extremely simple circuit construction. Another advantage
featured by the invention is that it is possible to adopt the
system according to the invention to various engines with different
fuel demand characteristics by an extremely simple measure of
merely varying the non-linear character of the non-linear means
producing a plurality of modified output components and the gains
for the respective modified output components to suit a given
engine fuel demand characteristic so as to exactly and faithfully
control the amount of fuel injected in accordance with the fuel
demand character of a particular engine. This means that the fuel
control system according to the invention has an extremely simple
requisite of merely varying the non-linear character of the
non-linear circuit means and the gains involved in the aforesaid
signal processing circuit for the compatibility with engines of
different ratings.
Consequently, this invention provides an excellent fuel control
system for internal combusion engines which eliminates the
drawbacks of the conventional fuel control system including that
which was disclosed by the U.S. Pat. No. 3,005,447 and has
hereinbefore been described.
Another object of the invention is to provide a fuel control system
for internal combustion engines, which further comprises two other
signal generators, in addition to the first signal generator, to
produce a voltage output corresponding to another operating
parameter of the engine for addition to the signal processing
circuit.
According to the second aspect of the invention, the pulse width of
the pulse signal impressed on the fuel injection valve, that is,
the amount of the fuel injected during the period of the pulse
width, may be increased by an amount corresponding to the output
voltage components for the output of the two signal generators.
This is an excellent advantage in that a desired engine output
torque may be produced when the engine is in a low temperature
condition and/or accelerating condition, at which time the fuel
supply should be increased.
BRIEF DESCRIPTION OF THE DRAWING
FIG. 1 is a block diagram of a preferred embodiment of the fuel
control system for internal combustion engines according to the
invention.
FIG. 2 is a schematic circuit diagram, partly in block form,
showing the principal part of the system of FIG. 1.
FIGS. 3 to 5 are graphs illustrating the operation of the system of
FIG. 1.
FIG. 6 is a schematic circuit diagram, partly in block form,
showing the principal part of a second embodiment of the system
according to the invention.
FIG. 7 is a schematic circuit diagram similar to FIG. 6 showing a
third embodiment of the system according to the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The invention will now be described in conjunction with a preferred
embodiment thereof with reference to the drawings.
Referring to FIG. 1, numeral 1 designates a first signal generator.
In this embodiment it is negative pressure signal generator to
produce an output voltage proportional to the negative pressure in,
for instance, a four-cylinder engine intake manifold (Not shown).
Numeral 2 designates a second signal generator to produce output
voltage in inverse proportion to the engine temperature. It is
actually a fuel increase signal generator to generate a fuel
increase signal when the engine is in a low temperature condition,
for instance when the engine temperature is below 40.degree. C, so
as to ensure smooth operation of the engine at low temperatures.
Numeral 3 designates a third signal generator. It is also a fuel
increase signal generator to generate a fuel increase signal on the
basis of the action of a switch, which is closed when the engine
intake negative pressure reaches a predetermined value, so as to
increase the fuel supply particularly under the high-load and
accelerating conditions of the engine for obtaining a desired
engine output torque. The voltage outputs of the first signal
generator 1 the second signal generator 2 and the third signal
generator 3 are fed to a signal processing section 4, which
produces output voltage e containing voltage components with
respective gains to the corresponding inputs (to be described
hereinafter in detail) Numeral 5 designates a switch constituting
an ignition start signal generator. It is operated (opened and
closed) synchronously with the fuel injection timing for the first
cylinder of the four-cylinder engine, for example. In synchronism
with the closure of the switch 5, a saw-tooth wave generator 6
generates a saw-tooth wave signal having a constant rise time. The
fuel injection cycle time for the first cylinder is indicated at T.
The saw-tooth wave voltage output of the saw-tooth wave generator 6
and the voltage output appearing at output terminal 4a of the
signal processing section 4 are fed to a pulse signal generator 7,
which produces a pulse signal with pulse width W corresponding to
the output voltage at the output terminal 4a. The pulse signal from
the pulse generator 7 is fed to a fuel injection valve drive 8,
which energizes an electromagnetic solenoid (not shown) of a fuel
injection valve 9 in response to the received pulse signal to drive
the fuel injection valve 9 such that it is held in the operative or
open position for a time interval equal to the pulse width W in
each fuel injection cycle. The fuel injection valve 9 is provided
in the first cylinder.
The switch 5, the saw-tooth wave generator 6, the pulse signal
generator 7, the fuel injection valve drive 8 and the fuel
injection valve 9 constitute a fuel injection subsystem for the
first cylinder. Similar subsystems are also provided to the
remaining second to fourth cylinders respectively, and the output
voltages appearing at output terminals 4b, 4c and 4d are similarly
added to the respective pulse signal generators.
The circuit construction of the signal processing section 4 is
shown in detail in FIG. 2. Referring to FIG. 2, numeral 10
designates an operational amplifier, numeral 11 a feedback resistor
(with resistance R) to provide for the negative feedback from the
output side to the input side of the operational amplifier 10,
numerals 12 to 14 gain correction variable resistors connected to a
common point at one end and to the earth at the other end, numeral
15 a gain adjustment resistor (with resistance R1) connected
between a movable tap 12a of the variable resistor 12 and the input
terminal of the operational amplifier 10, numeral 16 a gain
correction constant-voltage diode connected between the movable tap
12a and the earth, numeral 17 a gain adjustment resistor with
resistance R2 connected between a movable tap 13a of the variable
resistor 13 and the input terminal of the operational amplifier 10,
numeral 19 a gain correction constant-voltage diode connected
between a movable tap 14a of the variable resistor 14 and a gain
adjustment resistor (with resistance R3), which is in turn
connected to the input terminal of the operational amplifier 10,
numeral 20 a potential adjustment variable resistor with its
movable tap 20a connected through a gain adjustment resistor 21
(with resistance R4) to the input terminal of the operational
amplifier 10, numeral 22 a gain adjustment resistor (with reistance
R5) connected between the output terminal of the second signal
generator 2 and the input terminal of the operational amplifier 10,
and numeral 23 a gain adjustment resistor (with resistance R6)
connected between the output terminal of the third signal generator
3 and the input terminal of the operational amplifier 10. The ratio
of the components of the voltage output from the operational
amplifier 10 to the respective voltage outputs from the first to
third signal generators 1 to 3 depends upon the ratio between the
resistance R of the feedback resistor to each of the resistance R1,
R2, R3, R4, R5 and R6 of the respective gain adjustment resistors
15, 17, 19, 21, 22 and 23.
To describe the operation of the fuel control system of the above
construction according to the invention, it is assumed that the
fuel demand characteristic of the engine is given by a curve A-B as
shown in FIG. 3, where the ordinate represents the fuel amount Q to
be injected in one fuel injection cycle and the abscissa represents
the engine intake negative pressure -P (mm Hg). The curve A-B
represents the normal fuel demand characteristic without requiring
an additional increase of fuel supplied. If the engine intake
pressure P builds up beyond point P.sub.1 with increase in the
engine load, the fuel demand characteristic given by curve A-B is
replaced with a fuel demand characteristic given by curve C-D,
according to which the amount of fuel to be injected is increased
by an amount Q.sub.1 with respect to that according to the
characteristic of curve A-B for the same intake negative pressure.
When the absolute value of the intake negative pressure becomes
lower than P.sub.1, the characteristic of curve A-B is recovered.
Meanwhile, if the engine temperature is below, for instance,
40.degree. C, the fuel supply is increased by an additional amount
Q.sub.2 over the entire range of the engine intake negative
pressure, thus replacing the fuel demand characteristics given by
curves A-B and C-D with shifted fuel demand characteristics as
represented by dashed curves A'-B' and C'-D'. When the engine
temperature exceeds, for instance, 40.degree. C the characteristics
of curves A-B and C-D become available again.
The fuel amount Q to be injected is proportional to the period,
during which the fuel injection valve is held in the operative or
open position, and which depends upon the output voltage e produced
by the signal processing section 4. Thus, it is desirable that the
output characteristics for the output voltage e produced by the
signal processing section 4 are similar to the fuel demand
characteristics of FIG. 3 for the fuel amount Q to be injected, as
shown in FIG. 4. However, a voltage output characteristic identical
with the curve A-B cannot be obtained over the entire range of the
intake negative pressure in whatever way, so long as the output
voltage produced by the negative pressure signal generator 1 is
applied to the operational amplifier 10 only through the path of
the gain correction variable resistor 13 and the gain adjustment
resistor 17. Accordingly, the characteristic of curve A-B is
approximated by a plurality of linear portions, for instance three
portions A-F, F-E and E-B as shown in FIG. 4. In each portion, the
relation between the voltage e and intake negative pressure is
linear. The characteristic AFEB can be obtained by adding together
a linear voltage varying in proportion at a certain proportionality
constant to the intake negative pressure and a non-linear voltage,
which varies in proportion to the intake negative pressure at a
certain proportionality constant until the intake negative pressure
reaches a predetermined value and at another proportionality
constant when the predetermined value of the intake negative
pressure is exceeded. To describe this point in further detail, a
first voltage e'.sub.1, which is proportional to the intake
negative pressure, is obtained through the circuit of the gain
correction variable resistor 13 and gain adjustment resistor 17, a
second voltage e'.sub.2, which is constant when the intake negative
pressure is less than P.sub.1 and varies in proportion to the
negative pressure when the negative pressure is greater than
P.sub.1, is obtained through the circuit of the gain correction
variable resistor 12 and gain correction constant-voltage diode 16,
and a third voltage e'.sub.3, which is constant when the intake
negative pressure is greater than P.sub.2 and varies in proportion
to the negative pressure when the negative pressure is less than
P.sub.2, is obtained through the circuit of the gain correction
constant-voltage diode 18 and gain adjustment resistor 19. The
relationship between the input voltage e' to the operational
amplifier 10 and the engine intake negative pressure -P (mm Hg) is
shown in FIG. 5. In the Figure, plot H-I represents the first
voltage e'.sub.1, plot G-F-K represents the second voltage
e'.sub.2, and plot G-L represents the third voltage e'.sub.3. Point
E (corresponding to point E in FIG. 4) is determined by the
breakdown voltage of the gain correction constant-voltage diode 18
and the resistance of the gain correction variable resistor 14, and
point F (corresponding to point F in FIG. 4) is determined by the
breakdown voltage of the gain correction constant-voltage diode 16
and the resistance of the gain correction variable resistor 12. The
first, second and third input voltages e'.sub.1, e'.sub.2 and
e'.sub.3 are respectively amplified by the ratios of R/R.sub.2,
R/R.sub.1 and R/R.sub.3 and then accumulated with a resultant
output e through the operational amplifier 10. It will be
appreciated that by suitably setting the values of R.sub.2,R.sub.1
and R.sub.3 the slope of the curve showing the output voltage e of
the signal processing section 4 versus the engine intake negative
pressure may be made to approximate the curve A-B over the entire
pressure range. As the pulse width of the pulse output from the
pulse signal generator 7 varies in proportion to the output voltage
e from the operational amplifier 10, the amount of fuel supply to
the engine can faithfully follow the fuel demand characteristic
represented by the curve A-B in FIG. 3. In FIG. 5, plot M-N
represents a potential correction voltage (corresponding to a
fourth voltage) given by the potential adjustment resistor 20, plot
O-R an output voltage (corresponding to a fifth voltage) from the
temperature detection fuel increase signal generator 2, and plot
S-T an output voltage (corresponding to a sixth voltage) from the
pressure detection fuel increase signal generator 3. The potential
correction voltage given by the potential adjustment resistor 20,
which corresponds to the fourth input voltage e'.sub.4 with a gain
determined by R/R.sub.4, is also fed together with the first,
second and third input voltages e'.sub.1, e'.sub.2 and e'.sub.3 to
the operational amplifier 10, and it contributes a constant output
voltage component to the output voltage of the operational
amplifier 10 over the entire pressure range, as indicated at
e.sub.3 in FIG. 4.
When the engine temperature is below a predetermined value, for
instance 40.degree. C, the temperature detection fuel increase
signal generator 2 provides an output voltage, which gives rise to
the fifth input voltage e'.sub.5 determined by R/R.sub.5 for
impression together with the first to fourth input voltages
e'.sub.1, e'.sub.2, e'.sub.3 and e'.sub.4 on the operational
amplifier 10. As a result, the curve A-B for the fuel demand
characteristic is shifted to establish a new curve A'-B' over the
entire range of the engine intake negative pressure. Thus, the
output voltage e for the same negative pressure is increased by an
amount e.sub.5 accounting for the fifth input voltage e'.sub.5.
This means an increase of the pulse width of the output pulse
produced by the pulse signal generator 7 by an amount corresponding
to the additional component e.sub.5 of the output voltage e from
the operational amplifier 10. In this manner, the engine may be
operated smoothly when the engine temperature is low, at which time
an increased amount of fuel should be supplied to the engine.
When the engine intake pressure P exceeds the value P.sub.1 in FIG.
3, the pressure detection fuel increase signal generator 3 produces
an output voltage, which gives rise to the sixth input voltage
e'.sub.6 determined by R/R.sub.6 for impression together with the
first to fourth input voltages e'.sub.1, e'.sub.2, e'.sub.3 and
e'.sub.4 on the operational amplifier 10. As a result, the curves
A-F and C-D for the fuel demand characteristic over a pressure
range higher than P.sub.1 are replaced with respective new curves
A'-F' and C'-D'. Thus, the output voltage e is increased by an
amount e.sub.6 accounting for the sixth input voltage e'.sub.6.
This also means an increase of the pulse width of the output pulse
produced by the pulse signal generator by an amount corresponding
to the additional component e.sub.6 of the output voltage from the
operational amplifier 10. In this manner, fuel supply may be
increased to increase the engine output torque when the engine load
is high and/or acceleration is applied to the engine.
The output characteristic of the signal processing section 4 may be
patterned after various fuel demand characteristics of different
engines by appropriately varying the resistance of the gain
correction variable resistors 12, 13 and 14, the breakdown voltage
of the constant-voltage diodes 16 and 18, the resistance of the
gain adjustment resistors 15, 17 and 19 and the resistance of the
feedback resistor 11 such that the output voltage e of the
operational amplifier 10 conforms to a given fuel demand
characteristic. In some cases, the number of parallel current paths
between the first signal generator 1 and the operational amplifier
10 may be increased or decreased to provide for a corresponding
number of slopes approximating to the respective part of a given
characteristic curve.
Although in the foregoing embodiment the first signal generator 1
is described as a negative pressure signal generator to generate
electric signals corresponding to the engine intake suction pipe
negative pressure, i.e., and electric signal corresponding to an
engine-operating parameter, it may be replaced with a signal
generator that produces an electric signal corresponding to a
different engine-operating parameter such as engine speed, throttle
opening and pressure in other parts of the engine. Also, the second
and third signal generators are not limited to the temperature
detection fuel increase signal generator 2 and the pressure
detection fuel increase signal generator 3 as in the preceding
embodiment, but other signal generators adopted to detect the
conditions for increasing the fuel supply from the engine speed and
throttle opening may be used as well. Further, the non-linear
element for deriving from the output voltage of first control
signal generator a plurality of voltages having non-linear relation
with said voltages is not limited to the constant-voltage diodes 16
and 18, but other types of operational amplifiers, transistors and
combinations of these elements may also be used.
FIG. 6 shows second embodiment of the system, in which the voltage
of the characteristic AFEB in FIG. 4 is obtained through
operational amplifiers. In this Figure, parts 1, 2, 3, 4, 11, 11a,
12, 12a, 13, 13a, 14, 14a, 15, 17, 20, 21, 22 and 23 are the same
as the corresponding ones described earlier in connection with FIG.
4. Numerals 30 and 40 designate operational amplifiers, numerals 31
and 41 feedback resistors provided for the feedback from the output
side to the input side of the respective operational amplifiers 30
and 40, and numerals 32 and 33 adjustment resistors determining the
voltage level of one input to the respective operational amplifiers
30 and 40. The other input to the operational amplifiers are
obtained by correcting the voltage produced by the first signal
generator in proportion to the intake negative pressure through
respective gain correction variable resistors 12 and 14.
The operational amplifier 30 provides an output corresponding to
the difference between the two inputs. When one of the input
voltages is sufficiently large compared to the other input voltage
determined by the adjustment resistor 32, the output voltage is not
greater than the source voltage. Thus, the output voltage is
constant when the intake negative pressure is greater than a
predetermined value. In this way, the voltage appearing through the
gain correction resistor 15 may have a characteristic GFK as shown
in FIG. 5. In the operational emplifier 40, when one of the input
voltages is sufficiently large compared to the other input voltage
determined by the adjustment resistor 33, the output is reduced to
the source voltage (which is zero in this case), so that the
voltage appearing through the gain correction resistor 19 may have
a characteristic GEK in FIG. 5.
FIG. 7 shows a third embodiment of the system according to the
invention, in which the voltage of the characteristic AFEB in FIG.
4 is obtained. In FIG. 7, the same parts as those in FIG. 2 are
designated by like reference numerals. Numeral 40 designates an
n-p-n transistor, numeral 50 a p-n-p transistor, numerals 41 and 51
adjustment resistors determining the base potential on the
respective transistors 40 and 50, numerals 42 and 52 are auxiliary
resistors respectively determining the collector potential on the
transistor 40 and the emitter potential on the transistor 50, and
numerals 43 and 53 diodes. By presetting the resistance of the
resistor 41 the collector-emitter current in the transistor 40 is
determined to determine the voltage drop across the resistor 42.
Similarly, by presetting the resistance of the resistor 51 the
emitter-collector current in the transistor 50 to determine the
voltage drop across the resistor 52.
When the intake negative pressure is greater than the predetermined
value P.sub.1, the anode potential on the diode 43 is greater than
the cathode potential thereon, that is voltage drop across the
resistor 42, so that current flows through the diode 43. When the
intake negative pressure becomes small enough, current ceases to
flow from the anode to the cathode of the diode 43. In this way,
the voltage appearing through the gain correction resistor 15 may
have a characteristic GFK in FIG. 5. When the cathode side voltage
on the diode 53, that is, the intake negative pressure voltage, is
great, the cathode potential on the diode 53, that is voltage drop
across the resistor 52, is surpassed, so that current flows. When
the intake negative pressure is redued, current ceases. Thus, the
voltage appearing across the gain correction resistor 19 may have a
characteristic GEK in FIG. 5. The invention is not limited to the
four-cylinder cylinder engine as in the above embodiment, but it
may also be applied to the single-cylinder engine, two-cylinder
engine, three-engine engine and engines having five or more
cylinders.
As has been described in the foregoing, according to the first
feature of the invention, with the provision of a first signal
generator for producing a voltage output corresponding to an
operating parameter of the engine, non-linear circuit means for
modifying the output of the first signal generator so as to
introduce a non-linear characteristic approximating the fuel demand
characteristic of the engine by deriving from the output of the
first signal generator a plurality of modified output voltages
through respective non-linear circuit means, each of the plurality
of modified output voltages corresponding to each of a plurality of
subdivided parts of the engine fuel demand characteristic over the
entire range of the involved engine-operating parameter, and an
operational amplifier which receives the plurality of modified
output voltages and whose gains for the modified output voltages
are adjusted according to the subdivided parts of the fuel demand
characteristic of the engine to produce an output voltage covering
to be the entire range of the fuel demand characteristic of the
engine for varying the pulse width of a pulse signal impressed on
the fuel injection valve, it is possible that the pulse width of
the pulse signal impressed on the fuel injection valve can be
continually and exactly varied in accordance with the engine fuel
demand characteristic which is a non-linear function of an engine
operating parameter over the entire range thereof. Thus, it is
possible to exercise exact control of the amount of fuel supplied
to the engine in accordance with the fuel demand characteristic
thereof with a circuit of extremely simple construction. Also, it
is possible to apply the output voltage of the first signal
generator to various engines with different fuel demand
characteristics by an extremely simple measure of adjusting the
non-linear characteristic of the non-linear means and the gains of
the operational amplifier for the respective modified output
voltages to suit a given engine fuel demand characteristic of each
of the engines so as to exactly and faithfully control the pulse
width of the pulse signal to be impressed on the fuel injection
valve, that is, the amount of the fuel to be injected which meets
the fuel demand characteristic. In other words, the fuel control
system according to the invention has an extremely simple measure
of merely varying the non-linear characteristic of the non-linear
circuit means and the gains of the operational amplifier employed
to thereby obtain the compatibility with engines of different
ratings.
Furthermore, according to the second feature of the invention with
the provision of a second signal generator to detect the phenomenon
requiring an increase of the fuel to be injected, and the voltage
output of the second signal generator is added to the afore-said
signal processing circuit, so that in addition to the effects
obtainable according to the first feature of the invention it is
also possible to increase the pulse width of the pulse signal
impressed on the fuel injection valve, that is, the amount of the
fuel injected, by an amount corresponding to the output voltage of
the second signal generator, which is an excellent advantage in
that a desired engine output torque may be produced when the engine
is under a low temperature condition and/or an accelerating
condition requiring a increase of the fuel supply.
* * * * *